Triggering sequence of large aftershocks of the Mid Niigata prefecture, Japan Earthquake in 2004 by static stress changes

Masatoshi Miyazawa,Takuo Shibutani,Shiro Ohmi,Yoshihisa Iio,Kin’Ya Nishigami,Hiroshi Katao,Jim Mori,Satoshi Matsumoto

doi:10.1186/bf03351890

Masatoshi Miyazawa, Takuo Shibutani + Show 6 more

Open Access

https://doi.org/10.1186/bf03351890

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Abstract

AbstractFollowing the Mid Niigata prefecture Earthquake (MJMA6.8) in 2004, 4 large aftershocks (MJMA6.3, 6.0, 6.5, 6.1) occurred: three within 40 minutes and one after 4 days. We examine the possibility for the triggering of this sequence of large aftershocks by static stress changes. For the close spatial triggering, it is important to have information about the fault geometries, slip distribution, and focal mechanisms. We determine the fault plane orientations from the aftershock distributions. Slip distributions of the mainshock and the largest aftershock are obtained by seismic waveform inversions of local strong-motion records. Mechanisms for the events are taken from MT solutions. The temporal variations of Coulomb failure function changes (Δ CFF) are calculated on the fault planes of the aftershocks before their rupture. Positive Δ CFF values (0.06–0.3 MPa) are obtained around the hypocenters on the fault planes, indicating the possibility that static triggering from the main event and following aftershocks can explain the occurrence of subsequent aftershocks.

Highlights

IntroductionOccurred at the depth of 11 km in central Japan on October 23, 2004 (17:56 UT+09), and was followed by 4 relatively large (≥MJMA 6) aftershocks (Table 1)
The 2004 Mid Niigata prefecture Earthquake (MJMA 6.8)occurred at the depth of 11 km in central Japan on October 23, 2004 (17:56 UT+09), and was followed by 4 relatively large (≥MJMA 6) aftershocks (Table 1)
We consider slip distributions on these fault planes, similar to Toda and Stein (2003) who explained static triggering of a MJMA 6.4 event by the neighboring MJMA 6.6 event two month before, in southwest Kyushu, Japan in 1997

Summary

Introduction

Occurred at the depth of 11 km in central Japan on October 23, 2004 (17:56 UT+09), and was followed by 4 relatively large (≥MJMA 6) aftershocks (Table 1). In order to calculate the temporal static stress changes by examining CFF due to fault dislocations, the focal mechanism and slip distribution are needed. For the two largest events, the mainshock (MJMA 6.8) and the largest aftershock (MJMA 6.5), an assumption of uniform slip over an assumed fault area is inappropriate. We consider slip distributions on these fault planes, similar to Toda and Stein (2003) who explained static triggering of a MJMA 6.4 event by the neighboring MJMA 6.6 event two month before, in southwest Kyushu, Japan in 1997. For the remaining three aftershocks, we assume a uniform slip, because they have small fault areas compared to the two other larger events, and for the focal mechanism we use the Moment Tensor (MT) solutions by the National Research Institute for Earth Science and Disaster Prevention (NIED) (Table 1)

Slip Distributions of Mainshock and Largest Aftershock

Temporal Static Stress Changes

Discussion and Conclusions